The term "polyphenylene ether resin" includes a family of polymers well known to those skilled in the art, and they are made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the polyphenylene ethers are disclosed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. In the Hay patents, the polyphenylene ethers are prepared by an oxidative coupling reaction comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. Other disclosures relating to processes using metal-amine catalyst are found in Bussink et al, U.S. Pat. Nos. 3,337,499; Blanchard et al., 3,219,626; Laakso et al., 3,342,892; Borman, 3,344,116; Hori et al, 3,384,619; Faurote et al., 3,440,217; and disclosures relating to metal based catalysts which do not include amines, are known from patents such as Wieden et al, U.S. Pat. Nos. 3,442,885 (copper-amidines); Nakashio et al., 3,573,257 (metal-alcoholate or -phenolate); Kobayashi et al., 3,455,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to non-catalytic processes, such as oxidation with lead dioxide, silver oxide, etc. are described in Price et al, U.S. Pat. No. 3,382,212. All of the above-mentioned disclosures are incorporated herein by reference.
The term "alkenyl aromatic addition polymer" includes polymers and copolymers of alkenyl aromatic monomers such as styrene, alpha methyl styrene, chlorostyrene, ethylvinylbenzene, divinylbenzene, vinylnaphthalene and the like.
Most of the prior art processes for preparing compositions of alkenyl aromatic addition polymers and polyphenylene ether resins have been based on powder blending followed by several extrusions to form the alloyed material which is suitable for the injection molding of useful articles. The prior art has also employed solution blending techniques to form powder compositions suitable for extrusion blending. This procedure is carried out by first dissolving the components in a suitable solvent and thereafter adding a non-solvent to cause precipitation of both components. The polymeric components are prepared separately and are obtained in substantially pure form by various separation techniques and are thereafter dissolved in an appropriate solvent.
Such procedures have disadvantages, including a high energy cost, the need to use complex equipment, a loss in yield due the number of handling steps required, loss of economy through solvent and non-solvent evaporation and intermingling, and difficulty in controlling particle size distribution in the product.
It has now been discovered that resinous compositions of a polyphenylene ether resin component and an alkenyl aromatic addition polymer can be obtained by first polymerizing the polyphenylene ether resin in the alkenyl aromatic monomer. Thereafter, the alkenyl aromatic monomer is polymerized in the presence of the polyphenylene ether resin to form the composition.
An advantage of this process resides in the fact that these compositions may be injection molded after a single pass through an extruder. It is especially advantageous when compositions are prepared which have a high content of alkenyl aromatic addition polymers. Lower extrusion temperatures or increased extrusion rates are made possible when high proportions of alkenyl aromatic addition polymers are used.
The advantages over conventional antisolvent precipitation or solution blending are:
(i) the cost of the antisolvent and of recovering the antisolvent from the filtrate is eliminated;
(ii) the cost of independently isolating the alkenyl aromatic addition polymer from its reaction solvent is eliminated;
(iii) the cost of independently isolating the polyphenylene ether resin from its reaction mixture is eliminated;
(iv) no solvent separation procedure is required to directly obtain a blend composition of the alkenyl aromatic addition polymer and polyphenylene ether resin.
A surprising and unexpected result from the process of the present invention is the substantially complete elimination of colored impurities produced in the oxidation of the phenolic monomer. The reactions causing the colored impurities which are usually dark-reddish brown are not known, but it has been found that the subsequent bulk or suspension polymerization of the alkenyl aromatic monomer results in a colorless blend. This type of blend is particularly desirable for formulating white or pastel-colored molding powders. It has also been found that the subsequent bulk polymerization of the alkenyl aromatic monomer with e.g., a peroxide catalyst will result in the formation of graft copolymers of polyphenylene ether-alkenyl aromatic addition polymer.